From 6f4da14ee21429de5e2222caecd8d07a9b74144c Mon Sep 17 00:00:00 2001
From: ownedbywuigi <ownedbywuigi@gmail.com>
Date: Sat, 28 Mar 2026 07:34:59 +0000
Subject: [PATCH] Add JIT warm-up threshold preferences for baseline and ion
 compilation

---
 js/xpconnect/src/XPCJSContext.cpp | 21 +++++++++++++++++++--
 modules/libpref/init/all.js       |  5 +++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/js/xpconnect/src/XPCJSContext.cpp b/js/xpconnect/src/XPCJSContext.cpp
index e93854a9f9..3ca3da6b8b 100644
--- a/js/xpconnect/src/XPCJSContext.cpp
+++ b/js/xpconnect/src/XPCJSContext.cpp
@@ -1426,6 +1426,10 @@ ReloadPrefsCallback(const char* pref, void* data)
     bool useBaselineEager = Preferences::GetBool(JS_OPTIONS_DOT_STR
                                                  "baselinejit.unsafe_eager_compilation");
     bool useIonEager = Preferences::GetBool(JS_OPTIONS_DOT_STR "ion.unsafe_eager_compilation");
+    int32_t baselineWarmUpThreshold = Preferences::GetInt(JS_OPTIONS_DOT_STR
+                                                          "baselinejit.threshold", -1);
+    int32_t ionWarmUpThreshold = Preferences::GetInt(JS_OPTIONS_DOT_STR
+                                                     "ion.threshold", -1);
 
     sDiscardSystemSource = Preferences::GetBool(JS_OPTIONS_DOT_STR "discardSystemSource");
 
@@ -1472,10 +1476,23 @@ ReloadPrefsCallback(const char* pref, void* data)
 
     JS_SetParallelParsingEnabled(cx, parallelParsing);
     JS_SetOffthreadIonCompilationEnabled(cx, offthreadIonCompilation);
+
+    // -1 means "use engine default".
+    if (baselineWarmUpThreshold < -1)
+        baselineWarmUpThreshold = -1;
+    if (ionWarmUpThreshold < -1)
+        ionWarmUpThreshold = -1;
+
+    // Eager compilation prefs still override threshold prefs.
+    if (useBaselineEager)
+        baselineWarmUpThreshold = 0;
+    if (useIonEager)
+        ionWarmUpThreshold = 0;
+
     JS_SetGlobalJitCompilerOption(cx, JSJITCOMPILER_BASELINE_WARMUP_TRIGGER,
-                                  useBaselineEager ? 0 : -1);
+                                  baselineWarmUpThreshold);
     JS_SetGlobalJitCompilerOption(cx, JSJITCOMPILER_ION_WARMUP_TRIGGER,
-                                  useIonEager ? 0 : -1);
+                                  ionWarmUpThreshold);
     JS_SetGlobalJitCompilerOption(cx, JSJITCOMPILER_UNBOXED_OBJECTS,
                                   unboxedObjects);
     JS_SetGlobalJitCompilerOption(cx, JSJITCOMPILER_ION_INLINING,
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 5b60e0fabe..d0fe3e38d3 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -1265,6 +1265,11 @@ pref("javascript.options.unboxed_objects",  false);
 pref("javascript.options.baselinejit",      true);
 pref("javascript.options.ion",              true);
 pref("javascript.options.ion.inlining",     true);
+// JIT warm-up thresholds (-1 keeps engine defaults).
+// Lower values can improve sustained throughput on large script bundles
+// (e.g. React/jQuery-heavy apps) at some startup compile cost.
+pref("javascript.options.baselinejit.threshold", 8);
+pref("javascript.options.ion.threshold", 80);
 pref("javascript.options.asmjs",            true);
 pref("javascript.options.wasm",             true);
 // wasm jit crashes in 32bit builds because of 64bit casts so